ATP-sensitive K+ channels in pig urethral smooth muscle cells are heteromultimers of Kir6.1 and Kir6.2.
The inwardly rectifying properties and molecular basis of ATP-sensitive K(+) channels (K(ATP) channels) have now been established for several cell types. However, these aspects of nonvascular smooth muscle K(ATP) channels still remain to be defined. In this study, we investigated the molecular basis of the pore of K(ATP) channels of pig urethral smooth muscle cells through a comparative study of the inwardly rectifying properties, conductance, and regulation by PKC of native and homo- and heteroconcatemeric recombinant Kir6.x channels coexpressed with sulfonylurea receptor subunit SUR2B in human embryonic kidney (HEK) 293 cells by the patch-clamp technique (conventional whole-cell and cell-attached modes). In conventional whole-cell clamp recordings, levcromakalim (> or = 1 microM) caused a concentration-dependent increase in current that demonstrated strong inward rectification at positive membrane potentials. In cell-attached mode, the unitary amplitude of levcromakalim-induced native and recombinant heteroconcatemeric Kir6.1-Kir6.2 K(ATP) channels also showed strong inward rectification at positive membrane potentials. Phorbol 12,13-dibutyrate, but not the inactive phorbol ester, 4alpha-phorbol 12,13-didecanoate, enhanced the activity of native and heteroconcatemeric K(ATP) channels at -50 mV. The conductance of the native channels at approximately 43 pS was consistent with that of heteroconcatemeric channels with a pore-forming subunit composition of (Kir6.1)(3)-(Kir6.2). RT-PCR analysis revealed the expression of Kir6.1 and Kir6.2 transcripts in pig urethral myocytes. Our findings provide the first evidence that the predominant K(ATP) channel expressed in pig urethral smooth muscle possesses a unique, heteromeric pore structure that differs from the homomeric Kir6.1 channels of vascular myocytes and is responsible for the differences in inward rectification, conductance, and PKC regulation exhibited by the channels in these smooth muscle cell types.
Teramoto
Noriyoshi
N
Dept. of Pharmacology, Graduate School of Medical Sciences, Kyushu Univ., 3-1-1 Maidashi, Higashi Ward, Fukuoka, 812-8582, Japan. noritera@med.kyushu-u.ac.jp
Zhu
Hai-Lei
HL
Shibata
Atsushi
A
Aishima
Manami
M
Walsh
Emma J
EJ
Nagao
Masaya
M
Cole
William C
WC
D000818:Animals; D019806:Cromakalim / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005260:Female; D054086:KATP Channels; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D032389:Myocytes, Smooth Muscle / Q000166:cytology / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology; D024661:Potassium Channels, Inwardly Rectifying / Q000187:drug effects / Q000378:metabolism*; D011493:Protein Kinase C / Q000378:metabolism; D055503:Protein Multimerization; D013552:Swine; D014521:Urethra / Q000166:cytology / Q000378:metabolism*; D014665:Vasodilator Agents / Q000494:pharmacology; D000099161:Kcnj11 Channel
D019806:Cromakalim; D054086:KATP Channels; D015240:Phorbol 12,13-Dibutyrate; D024661:Potassium Channels, Inwardly Rectifying; D011493:Protein Kinase C; D014665:Vasodilator Agents; D000099161:Kcnj11 Channel; C092520:uK-ATP-1 potassium channel